HIV infection has emerged as a major public health problem among African Americans in rural regions of the Southeastern United States, where the epidemics of gonorrhea, syphilis, and other curable STDs have also escalated. Evidence suggests that an increasing proportion of HIV infection in this population is transmitted through heterosexual contact. A substantial and rising proportion of HIV+ people in some predominantly black communities report no high risk behavior other than unprotected heterosexual contact with a limited number of partners. Little information has been published concerning risk factors for HIV and other STDs among rural African Americans. Since mounting evidence suggests that treatable STDs facilitate the spread of HIV infection, it seems likely that the high prevalence of STDs among African Americans contributes substantially to HIV transmission in this population and that reducing STD prevalence may lower the incidence of HIV infection. We propose a population-based case-control study in 13 rural North Carolina counties to test the following hypotheses: l) At least 30% of newly reported cases of HIV infection among African Americans in rural North Carolina acquired their infection through heterosexual transmission with a limited number of partners during the preceding year; 2) At least 25% of heterosexually transmitted HIV infections in this population can be attributed to curable STDs. Cases will be 200 African Americans from these counties who are reported to the NC HIV/STD Control Branch as having acquired HIV infection through heterosexual transmission. Department of Motor Vehicles drivers license files will be used to randomly select 200 population-based controls. Subjects will be recruited over a 42 month period. After study nurses obtain informed consent, subjects will be asked to complete a standardized questionnaire concerning risk behaviors and STD history and provide blood specimens for syphilis testing: Data analysis will compare frequency of reactive syphilis serology and types and frequency of STDs and high risk behaviors reported among cases and controls. Stratified analysis and multiple logistic regression will investigate associations of HIV serostatus with risk behaviors and STDs after controlling for potential confounders. The population attributable risk will be used to quantify the potential impact of bacterial STDs on risk of HIV infection. The proposed study has the potential to advance our understanding of the epidemiology of HIV infection among rural African Americans and will provide data for intervention studies concerning the efficacy of enhanced STD diagnosis and treatment as a strategy of reducing HlV transmission in this population. These data will assist us in developing effective HIV prevention programs for rural African Americans.